1. Field of the Invention
This invention relates to a reduced molecular weight native gellan gum.
2. Description of the Related Art
Gellan gum is a high molecular weight polysaccharide produced by fermentation. The constituent sugars of gellan gum are glucose, glucuronic acid and rhamnose in the molar ratio of 2:1:1. These sugars are linked together to give a primary structure consisting of a linear tetrasaccharide repeat unit as shown below: ##STR1##
In gellan gum's native or high acyl form, two acyl substituents, acetate and glycerate, are present. Both substituents are located on the same glucose residue, and on average, there is one glycerate per repeat unit and one acetate every two repeat units.
Gums are primarily used to thicken or gel water and are frequently classified into two groups: thickeners and gelling agents. Typical thickeners include starches, guar gum, carboxymethylcellulose, alginate, methylcellulose, gum karaya and gum tragacanth. Common gelling agents include gelatin, starch, alginate, pectin, carrageenan, agar and methylcellulose.
Gelling agents are used by the food industry in a variety of applications, including confectionery jellies, jams and jellies, dessert gels, icings and dairy products. Gelling agents differ in the conditions under which they can be used as well as in the texture of the gels they form. These distinctive properties of gels have led to the exclusive use of certain gelling agents in a number of products (e.g., starch in confectionery jellies; gelatin in capsules; agar in icings; and alginate in pimento strips).
Gels can be formed in a number of ways. Gels which form upon cooling a hot solution of the gelling agent are classified as thermally setting gels. Typical thermally setting gels include gelatin, blends of xanthan gum and locust bean gum, and agar. Gels which require addition of ions to the gelling agent solution in order to set are classified as ionic setting gels. Common ionic setting gels include alginate, kappa carrageenan, low methoxy pectin and gellan gum.
Generally, ionic setting gels are ion specific. For example, alginate and low methoxy pectin both require the presence of Ca.sup.2+ ions in order to gel, while kappa carrageenan will gel only in the presence of K.sup.+ ions. Gellan gum is unique among ionic setting gelling agents because it forms gels with almost all ions, including hydrogen ions.
Perhaps the most familiar gelling agent is gelatin, which is used to prepare, among other products, dessert gels that are popular in many parts of the world. Unlike polysaccharide gelling agents, gelatin is a protein derived from animal sources. Gelatin possesses many desirable characteristics, including a melting temperature below body temperature. Consequently, gels made from gelatin melt in the mouth; this characteristic provides enhanced organoleptic properties.
However, many consumers today are interested in food products which are free from ingredients derived from animal sources. Consequently, it would be desirable to provide a gelling agent, derived from a non-animal source, which could be used in place of gelatin in selected food products.
Native gellan gum, which is produced by bacterial fermentation, forms gels that have a texture similar to that of gelatin gels. But solutions prepared with native gellan gum are highly viscous even at elevated temperatures. In addition, these solutions gel at high temperatures.